Fluorinated monomer, polymer, resist composition, and patterning process

ABSTRACT

A fluorinated monomer has formula (1) wherein R 1  is H, F, methyl or trifluoromethyl, R 2  and R 3  are H or a monovalent hydrocarbon group, R 4  to R 6  each are a monovalent fluorinated hydrocarbon group, A is a divalent hydrocarbon group, and k 1  is 0, 1 or 2. A polymer derived from the fluorinated monomer may be endowed with appropriate water repellency, water slip, acid lability and hydrolysis and is useful as an additive polymer in formulating a resist composition.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2010-088537 filed in Japan on Apr. 7, 2010,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to novel fluorinated monomers (or polymerizablecompounds) which are useful as raw materials for the synthesis offunctional, pharmaceutical and agricultural chemicals. In conjunctionwith a photolithography process for the microfabrication ofsemiconductor devices, and particularly to an immersion photolithographyprocess involving directing ArF excimer laser radiation having awavelength of 193 nm from a projection lens toward a resist-coatedsubstrate, with a liquid (e.g., water) intervening between the lens andthe substrate, the fluorinated monomer is useful in forming an additivepolymer to be added to formulate a radiation-sensitive resistcomposition having high transparency and improved developmentproperties.

This invention also relates to a polymer comprising recurring unitsderived from the fluorinated monomer, a photoresist compositioncomprising the polymer, and a process for forming a pattern using thephotoresist composition.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. The backgroundsupporting such a rapid advance is a reduced wavelength of the lightsource for exposure. The change-over from i-line (365 nm) of a mercurylamp to shorter wavelength KrF excimer laser (248 nm) enabled mass-scaleproduction of dynamic random access memories (DRAM) with an integrationdegree of 64 MB (processing feature size≦0.25 μm). To establish themicropatterning technology necessary for the fabrication of DRAM with anintegration degree of 256 MB and 1 GB or more, the lithography using ArFexcimer laser (193 nm) is under active investigation. The ArF excimerlaser lithography, combined with a high NA lens (NA≧0.9), is consideredto comply with 65-nm node devices. For the fabrication of next 45-nmnode devices, the F₂ laser lithography of 157 nm wavelength became acandidate. However, because of many problems including a cost and ashortage of resist performance, the employment of F₂ lithography waspostponed. ArF immersion lithography was proposed as a substitute forthe F₂ lithography (see Proc. SPIE Vol. 4690, xxix, 2002).

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water and ArF excimer laser is irradiatedthrough the water. Since water has a refractive index of 1.44 at 193 nm,pattern formation is possible even using a lens with NA of 1.0 orgreater. The theoretically possible maximum NA is 1.44. The resolutionis improved by an increment of NA. A combination of a lens having NA ofat least 1.2 with ultra-high resolution technology suggests a way to the45-nm node (see Proc. SPIE Vol. 5040, p 724, 2003).

The ArF immersion lithography has a possibility that water-solublecomponents in the resist film be leached in immersion water duringexposure. Specifically an acid generated during exposure and a basiccompound previously added to the resist material can be leached inimmersion water. As a result, pattern profile changes and patterncollapse can occur. It is also pointed out that if the resist film isless water repellent, water droplets remaining on the resist film afterscanning, though in a minute volume, can penetrate into the resist filmto generate defects. It was then proposed to provide a protectivecoating between the resist film and water to prevent resist componentsfrom being leached out and water from penetrating into the resist film,the process being referred to as “topcoat process.” See 2nd ImmersionWorkshop: Resist and Cover Material Investigation for ImmersionLithography, 2003.

In the ArF immersion lithography using a topcoat, a protective coatingmaterial which is soluble in alkaline developer is advantageous. Thiseliminates the step of stripping off the protective coating, offeringgreat cost and process merits. Thus, great efforts have been devoted todevelop water-insoluble resist protective coating materials, forexample, resins having alkali-soluble units such as fluorinated alcohol,carboxyl or sulfo groups, as described in JP-A 2006-91798.

On the other hand, a process for preventing resist components from beingleached out and water from penetrating into the resist film without aneed for a protective coating material has also been developed, theprocess being referred to as “topcoatless process”, as described in JP-A2007-187887. In the topcoatless process, an alkali-soluble hydrophobicpolymer is added to the resist material as a surfactant, whereupon thehydrophobic compound is segregated at the resist surface during resistfilm formation. The process is thus expected to achieve equivalenteffects to the use of resist protective coating material. Additionally,the process is economically advantageous over the use of a resistprotective film because steps of forming and removing the protectivefilm are unnecessary.

In either of the topcoat and topcoatless processes, the ArF immersionlithography requires a scanning speed of about 300 to 700 mm/sec inorder to gain higher throughputs. In the event of such high-speedscanning, if the water repellency of the resist or protective film isinsufficient, water droplets may be left on the film surface afterscanning. Residual droplets may cause defects. To eliminate suchdefects, it is necessary to improve the water repellency of the relevantcoating film and the flow or mobility of water (hereinafter, water slip)on the film. The film material must be designed so as to increase thereceding contact angle (see 2nd International Symposium on ImmersionLithography, 12-15 Sep. 2005, Defectivity data taken with a full-fieldimmersion exposure tool, Nakano et al). In connection with such polymerdesign, it is reported that introduction of fluorine is effective forimproving water repellency, and formation of micro-domain structure by acombination of different water repellent groups is effective forimproving water slip. See Progress in Organic Coatings, 31, p 97 (1997).

One exemplary material known to have excellent water slip and waterrepellency on film surface is a copolymer of α-trifluoromethylacrylateand norbornene derivative (Proc. SPIE Vol. 4690, p 18, 2002). While thispolymer was developed as the resin for F₂ (157 nm) lithography resistmaterials, it is characterized by a regular arrangement of molecules of(highly water repellent) α-trifluoromethylacrylate and norbornenederivative in a ratio of 2:1. When a water molecule interacts withmethyl and trifluoromethyl groups, there is a tendency that theorientation distance between water and methyl is longer. A resin havinga regular arrangement of both substituent groups is improved in waterslip because of a longer orientation distance of water. In fact, whenthis polymer is used as the base polymer in a protective coating forimmersion lithography, water slip is drastically improved (see US20070122736 or JP-A 2007-140446). Another example of the highly waterrepellent/water slippery material is a fluorinated ring-closingpolymerization polymer having hexafluoroalcohol groups on side chains.This polymer is further improved in water slip by protecting hydroxylgroups on side chains with acid labile groups, as reported in Proc. SPIEVol. 6519, p 651905 (2007).

Although the introduction of fluorine into resins is effective forimproving water repellency and water slip, the introduction of extrafluorine can induce new defects known as “blob defects”. Blob defectsare likely to form during spin drying after development, particularlywhen the film has a high surface contact angle after development. Oneapproach for suppressing blob defects is by introducing highlyhydrophilic substituent groups (e.g., carboxyl or sulfo groups) into aresin to reduce the surface contact angle after development. However,since these groups serve to reduce the water repellency and water slipof the resin, this approach is not applicable to high-speed scanning.There is a desire to have a resin material which can minimize blobdefects while maintaining highly water repellent and water slipproperties during immersion lithography.

The highly water repellent/water slippery materials discussed above areexpected to be applied not only to the ArF immersion lithography, butalso to the resist material for mask blanks. Resist materials for maskblanks are subject to long-term exposure in vacuum. It is pointed outthat sensitivity variations or profile changes can occur as an aminecomponent in the resist material is adsorbed to the resist film surfaceduring the long-term exposure. It was then proposed to add a compoundhaving surface active effect to modify the surface of a resist film forpreventing adsorption of amine to the resist film.

CITATION LIST

-   Patent Document 1: U.S. Pat. No. 7,455,952 (JP-A 2006-91798)-   Patent Document 2: JP-A 2007-187887-   Patent Document 3: US 20070122736 (JP-A 2007-140446)-   Non-Patent Document 1: Proc. SPIE Vol. 4690, xxix, 2002-   Non-Patent Document 2: Proc. SPIE Vol. 5040, p 724, 2003-   Non-Patent Document 3: 2nd Immersion Workshop: Resist and Cover    Material Investigation for Immersion Lithography (2003)-   Non-Patent Document 4: 2nd International Symposium on Immersion    Lithography, 12-15 Sep. 2005, Defectivity data taken with a    full-field immersion exposure tool, Nakano et al.-   Non-Patent Document 5: Progress in Organic Coatings, 31, p 97 (1997)-   Non-Patent Document 6: Proc. SPIE Vol. 4690, p 18 (2002)-   Non-Patent Document 7: Proc. SPIE Vol. 6519, p 651905 (2007)

SUMMARY OF INVENTION

An object of the invention is to provide a novel fluorinated monomer; apolymer derived therefrom and suited as an additive polymer in resistcompositions; a resist composition, especially chemically amplifiedpositive resist composition comprising the additive polymer so that thecomposition exhibits excellent water repellency and water slip and formsa resist pattern of satisfactory profile after development, the patternhaving few development defects; and a pattern forming process using thecomposition. The additive polymer used herein is highly transparent toradiation with wavelength of up to 200 nm. Various properties of thepolymer including water repellency, water slip, fat solubility, acidlability, and hydrolysis may be adjusted by a choice of polymerstructure. The monomer can be prepared from reactants which are readilyavailable and easy to handle.

The inventors have found that when a polymer having a plurality offluorinated alkylcarbonyloxy groups in recurring units is used as anadditive to formulate a resist composition, the resist composition formsa resist film which has sufficient water repellency and water slip towithstand high-speed scanning without a need for a resist protectivefilm. Since the polymer is susceptible to hydrolysis in alkalinedeveloper, the resist film surface after development is modifiedhydrophilic, which is effective for substantially reducing blob defects.

Accordingly, the present invention provides a fluorinated monomer, apolymer, a resist composition, and a pattern forming process, as definedbelow.

In a first aspect, the invention provides a fluorinated monomer havingthe general formula (1):

wherein R¹ is hydrogen, fluorine, methyl or trifluoromethyl, R² and R³are each independently hydrogen or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R² and R³ may bond together to form anon-aromatic ring with the carbon atom to which they are attached, R⁴ toR⁶ each are a C₁-C₆ monovalent fluorinated hydrocarbon group, A is astraight, branched or cyclic C₁-C₁₀ divalent hydrocarbon group, and k¹is an integer of 0 to 2.

In a second aspect, the invention provides a polymer comprisingrecurring units of the general formula (1a):

wherein R¹ to R⁶, A, and k¹ are as defined above.

In a third aspect, the invention provides a resist compositioncomprising (A) a polymer comprising recurring units of the generalformula (1a), (B) a polymer having a lactone ring-derived structure,hydroxyl-containing structure and/or maleic anhydride-derived structureas a base resin, said base polymer becoming soluble in alkalinedeveloper under the action of acid, (C) a compound capable of generatingan acid upon exposure to high-energy radiation, and (D) an organicsolvent.

A preferred embodiment provides a resist composition comprising (A) apolymer comprising recurring units of the general formula (1a) definedabove and recurring units of one or more type selected from the generalformulae (2a) to (2i), (B) a polymer having a lactone ring-derivedstructure, hydroxyl-containing structure and/or maleic anhydride-derivedstructure as a base resin, said base polymer becoming soluble inalkaline developer under the action of acid, (C) a compound capable ofgenerating an acid upon exposure to high-energy radiation, and (D) anorganic solvent.

Herein R¹ is as defined above, R^(4a) and R^(4b) each are hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, orR^(4a) and R^(4b) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon atom to which they are attached, R^(5a)is hydrogen, a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon or fluorinated hydrocarbon group, or an acid labile group,in the case of hydrocarbon group, any constituent moiety —CH₂— may bereplaced by —O— or —C(═O)—, R^(6a), R^(6b) and R^(6c) each are hydrogen,or a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group,R^(6a) and R^(6b), R^(6a) and R^(6c), or R^(6b) and R^(6c) may bondtogether to form a non-aromatic ring of 3 to 8 carbon atoms with thecarbon atom to which they are attached, R^(7a) is hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, R^(7b)is a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group,R^(7a) and R^(7b) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon and oxygen atoms to which they areattached, R^(8a) is a straight, branched or cyclic C₁-C₁₅ monovalentfluorinated hydrocarbon group, R^(9a) is a straight, branched or cyclicC₁-C₁₀ monovalent fluorinated hydrocarbon group, R^(10a) is a straight,branched or cyclic C₁-C₁₅ monovalent hydrocarbon group which may containhalogen or oxygen, and k² is 0 or 1.

In a preferred embodiment, the polymer (B) is selected from the groupconsisting of (meth)acrylate polymers (α-trifluoromethyl)acrylate-maleicanhydride copolymers, cycloolefin-maleic anhydride copolymers,polynorbornene, polymers resulting from ring-opening metathesispolymerization of cycloolefins, hydrogenated polymers resulting fromring-opening metathesis polymerization of cycloolefins,polyhydroxystyrene, copolymers of hydroxystyrene with one or more(meth)acrylate, styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,hydroxyvinylnaphthalene, hydroxyvinylanthracene, indene, hydroxyindene,acenaphthylene, or norbornadiene derivatives, and novolac resins.

In a preferred embodiment, the polymer (B) comprises recurring units ofat least one type selected from the general formulae (2A) to (2D).

Herein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA is anacid labile group, XB and XC each are a single bond or a straight orbranched C₁-C₄ divalent hydrocarbon group, YA is a substituent grouphaving a lactone structure, ZA is hydrogen, or a C₁-C₁₅ fluoroalkylgroup or C₁-C₁₅ fluoroalcohol-containing substituent group, and k^(1A)is an integer of 1 to 3.

Preferably the polymer (A) comprising recurring units of formula (1a) isadded in an amount of 0.1 to 50 parts by weight per 100 parts by weightof the polymer (B). The resist composition may further comprise (E) abasic compound and/or (F) a dissolution regulator.

In a fourth aspect, the invention provides:

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate to form a resistcoating, (2) heat treating the resist coating and exposing it tohigh-energy radiation through a photomask, and (3) developing theexposed coating with a developer;

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate to form a resistcoating, (2) heat treating the resist coating and exposing it tohigh-energy radiation from a projection lens through a photomask whileholding a liquid between the substrate and the projection lens, and (3)developing the exposed coating with a developer; or

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate to form a resistcoating, (2) forming a protective coating onto the resist coating, (3)heat treating the resist coating and exposing it to high-energyradiation from a projection lens through a photomask while holding aliquid between the substrate and the projection lens, and (4) developingwith a developer.

Most often the liquid is water. The high-energy radiation has awavelength in the range of 180 to 250 nm.

In a further aspect, the invention provides a pattern forming processcomprising the steps of (1) applying the resist composition definedabove onto a mask blank to form a resist coating, (2) heat treating theresist coating and exposing it in vacuum to electron beam, and (3)developing with a developer.

Advantageous Effects of Invention

The fluorinated monomer is useful as a raw material for the productionof functional, pharmaceutical, and agricultural chemicals and can beprepared from reactants which are readily available and easy to handle.The polymer derived therefrom is useful as an additive polymer toformulate a radiation-sensitive resist composition which has hightransparency to radiation having a wavelength of up to 500 nm,especially up to 300 nm and forms a resist pattern having fewdevelopment defects. The polymer is designed such that any of itsproperties including water repellency, water slip, fat solubility, acidlability and hydrolysis may be tailored by a choice of a properstructure.

DESCRIPTION OF EMBODIMENTS

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise. The notation (Cn-Cm) means agroup containing from n to m carbon atoms per group. The abbreviation“phr” is parts by weight per 100 parts by weight of the base resin.

While a certain compound is herein represented by a chemical formula,many compounds have a chemical structure for which there can existenantiomers or diastereomers. Each chemical formula collectivelyrepresents all such stereoisomers, unless otherwise stated. Suchstereoisomers may be used alone or in admixture.

Fluorinated Monomer

One embodiment of the invention is a fluorinated monomer having thegeneral formula (1).

Herein R¹ is hydrogen, fluorine, methyl or trifluoromethyl, R² and R³are each independently hydrogen or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R² and R³ may bond together to form anon-aromatic ring with the carbon atom to which they are attached, R⁴ toR⁶ each are a C₁-C₆ monovalent fluorinated hydrocarbon group, A is astraight, branched or cyclic C₁-C₁₀ divalent hydrocarbon group, and k¹is an integer of 0 to 2.

Examples of the straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon group represented by R² and R³ include, but are not limitedto, straight, branched or cyclic alkyl groups such as methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl,n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl,cyclohexylethyl, cyclohexylbutyl, norbornyl, oxanorbornyl,tricyclo[5.2.1.0^(2,6)]decanyl, and adamantyl; and substituted forms ofthe foregoing in which some hydrogen atoms are replaced by fluorine,hydroxyl, alkoxy, carboxy, alkoxycarbonyl, oxo or other radicals.

Examples of the non-aromatic ring (or alicyclic) that is formed by R²and R³ include, but are not limited to, the following.

Herein and throughout the specification, the broken line designates avalence bond.

Examples of the C₁-C₆ monovalent fluorinated hydrocarbon grouprepresented by R⁴ to R⁶ are given below, but not limited thereto.

Examples of the straight, branched or cyclic C₁-C₁₀ divalent hydrocarbongroup represented by A are given below.

Illustrative, non-limiting examples of the compound having formula (1)are given below.

Herein R¹ is as defined above.

The fluorinated monomer having formula (1) may be prepared through stepsi) and ii) according to the reaction scheme shown below although thepreparation method is not limited thereto.

Herein R¹ to R⁶, A and k¹ are as defined above. R⁷ is halogen, hydroxylor —OR⁹ wherein R⁹ is methyl, ethyl or a group of the formula (6):

wherein R⁴ is as defined above. R⁸ is halogen, hydroxyl or —OR¹⁰ whereinR¹⁰ is methyl, ethyl or a group of the formula (7):

wherein R¹, A and k¹ are as defined above.

In the case of k¹=1 in formula (1), an alternative process is possiblewhich starts with the reaction product of step i) and includes stepsiii) and iv) according to the reaction scheme shown below.

Herein R¹ to R⁶ and A are as defined above, R¹¹ is halogen, R¹² ishalogen, hydroxyl, alkoxy or acyloxy, and M^(a) is Li, Na, K, Mg_(1/2),Ca_(1/2) or substituted or unsubstituted ammonium.

Step i) is reaction of fluorinated alcohol (2) with acylating agent (3)to form cyclic hemi-orthoester compound (4).

In general, when a pinacol of formula (12) is subjected tomono-acylation using acylating agent (3), the equilibrium is biased infavor of a straight mono-acylated compound of formula (13). A cyclichemi-orthoester (14) is generally impossible to isolate althoughequilibrium in solution can be observed by NMR spectroscopy or the like.

Herein R⁴ and R⁷ are as defined above.

In the practice of the invention, when reaction was performed using analcohol (2) containing fluorinated alkyl as a substituent group on diol,hemi-orthoester (4) could be isolated in a pure and stable way. This isbecause hemi-orthoester (4) has a high degree of substitution withfluorinated hydrocarbon groups which serve as a strong electronattractive group so that the hemi-orthoester form may become stabilizedenough to isolate.

Notably the method for synthesizing fluorinated alcohol (2) which is thestarting compound for the synthesis of fluorinated monomer (1) isdescribed in JP-A 2007-204385. For example, a fluorinated alcohol (2)wherein R² and R³ are monovalent hydrocarbon groups can be synthesizedaccording to the following scheme.

Herein R² to R⁶ are as defined above, R¹⁴ is hydrogen or a straight,branched or cyclic C₁-C₆ monovalent hydrocarbon group, and M^(b) isoptionally substituted Li, Na, K, MgP, or ZnP wherein P is halogen.

The reaction of step i) may readily proceed in a well-known manner. Thepreferred acylating agent (3) is an acid chloride of formula (3) whereinR⁷ is chlorine or an acid anhydride of formula (3) wherein R⁷ is —OR¹¹.In one procedure using an acid chloride, a fluorinated alcohol (2), acorresponding acid chloride (e.g., trifluoroacetic acid chloride orpentafluoropropionic acid chloride), and a base (e.g., triethylamine,pyridine or 4-dimethylaminopyridine) are successively or simultaneouslyadded to a solventless system or to a solvent (e.g., methylene chloride,acetonitrile, diethyl ether, tetrahydrofuran, toluene or hexane), whilethe reaction system may be cooled or heated as desired. In anotherprocedure using an acid anhydride, a fluorinated alcohol (2), acorresponding acid anhydride (e.g., trifluoroacetic anhydride orpentafluoropropionic anhydride), and a base (e.g., triethylamine,pyridine or 4-dimethylaminopyridine) are successively or simultaneouslyadded to a solvent (e.g., methylene chloride, acetonitrile, diethylether, tetrahydrofuran, toluene or hexane), while the reaction systemmay be cooled or heated as desired. An appropriate amount of acylatingagent (3) used, which widely varies with other reaction conditions, is2.0 to 5.0 moles, more preferably 2.0 to 3.0 moles per mole of thestarting fluorinated alcohol (2). An appropriate amount of the baseused, which widely varies with other reaction conditions, is 2.0 to 5.0moles, more preferably 2.0 to 3.0 moles per mole of the startingfluorinated alcohol (2). The reaction time is determined as appropriateby monitoring the reaction process by gas chromatography (GC) or silicagel thin-layer chromatography (TLC) because it is desirable from theyield aspect to drive the reaction to completion. Usually the reactiontime is about 0.5 to about 10 hours. The desired hemi-orthoester (4) maybe obtained from the reaction mixture by ordinary aqueous work-up. Ifnecessary, the compound may be purified by standard techniques likedistillation and chromatography.

Step ii) is reaction between the hemi-orthoester (4) and an esterifyingagent (5) to form a fluorinated monomer (1).

The reaction may readily proceed in a well-known manner. The esterifyingagent (5) is preferably an acid chloride of formula (5) wherein R⁸ ischlorine or a carboxylic acid of formula (5) wherein R⁸ is hydroxyl. Inone procedure using an acid chloride, a hemi-orthoester (4), acorresponding acid chloride (e.g., methacryloyloxyacetic acid chloride),and a base (e.g., triethylamine, pyridine or 4-dimethylaminopyridine)are successively or simultaneously added to a solventless system or to asolvent (e.g., methylene chloride, acetonitrile, toluene or hexane),while the reaction system may be cooled or heated as desired. In anotherprocedure using a carboxylic acid, a hemi-orthoester (4) and acorresponding carboxylic acid (e.g., methacryloyloxyacetic acid) in asolvent (e.g., toluene or hexane) are heated in the presence of an acidcatalyst while water formed during reaction may be removed out of thesystem if desired. Suitable acid catalysts used herein include mineralacids such as hydrochloric acid, sulfuric acid, nitric acid andperchloric acid and organic acids such as p-toluenesulfonic acid andbenzenesulfonic acid.

Step iii) is reaction between a hemi-orthoester (4) and an esterifyingagent (8) to form a halo ester compound (9) when it is desired toproduce a fluorinate monomer of formula (1) wherein k¹=1.

The reaction may readily proceed in a well-known manner. The esterifyingagent (8) is preferably an acid chloride of formula (8) wherein R¹² ischlorine or a carboxylic acid of formula (8) wherein R¹² is hydroxyl. Inone procedure using an acid chloride, a hemi-orthoester (4), acorresponding acid chloride (e.g., 2-chloroacetic acid chloride or4-chlorobutyric acid chloride), and a base (e.g., triethylamine,pyridine or 4-dimethylaminopyridine) are successively or simultaneouslyadded to a solventless system or to a solvent (e.g., methylene chloride,toluene, hexane, diethyl ether, tetrahydrofuran or acetonitrile), whilethe reaction system may be cooled or heated as desired. In anotherprocedure using a carboxylic acid, a hemi-orthoester (4) and acorresponding carboxylic acid (e.g., 2-chloroacetic acid or4-chlorobutyric acid) in a solvent (e.g., toluene or hexane) are heatedin the presence of an acid catalyst while water formed during reactionmay be removed out of the system if desired. Suitable acid catalystsused herein include mineral acids such as hydrochloric acid, sulfuricacid, nitric acid and perchloric acid and organic acids such asp-toluenesulfonic acid and benzenesulfonic acid.

Step iv) is reaction between the halo-ester compound (9) and acarboxylic acid salt (10) to form a monomer (11), i.e., fluorinatedmonomer (1).

The reaction may be effected by a standard technique. The carboxylicacid salt (10) may be any of commercially available carboxylic acidsalts such as metal salts of various carboxylic acids as purchased.Alternatively, the carboxylic acid salt may be formed within thereaction system from a corresponding carboxylic acid such as methacrylicacid or acrylic acid and a base. An appropriate amount of carboxylicacid salt (10) used is 0.5 to 10 moles, more preferably 1.0 to 3.0 molesper mole of the reactant, halo-ester compound (9). If the amount ofcarboxylic acid salt (10) is less than 0.5 mole, a larger fraction ofthe reactant may be left unreacted, leading to a substantial drop ofpercent yield. More than 10 moles of carboxylic acid salt (10) may beuneconomical due to increased material costs and reduced pot yields. Inthe other embodiment where a carboxylic acid salt is formed within thereaction system from a corresponding carboxylic acid and a base,examples of the base used herein include amines such as ammonia,triethylamine, pyridine, lutidine, collidine, and N,N-dimethylaniline;hydroxides such as sodium hydroxide, potassium hydroxide, andtetramethylammonium hydroxide; carbonates such as potassium carbonateand sodium hydrogen carbonate; metals such as sodium; metal hydridessuch as sodium hydride; metal alkoxides such as sodium methoxide andpotassium tert-butoxide; organometallics such as butyllithium andethylmagnesium bromide; and metal amides such as lithiumdiisopropylamide. One or more bases may be selected from these examples.The amount of the base used is preferably 0.2 to 10 moles, and morepreferably 0.5 to 2.0 moles per mole of the corresponding carboxylicacid. If the amount of the base is less than 0.2 mole, a large fractionof the carboxylic acid may become a waste, which is uneconomical. Morethan 10 moles of the base may lead to a substantial drop of yield due toincreased side reactions.

Suitable solvents which can be used in step iv) include hydrocarbonssuch as toluene, xylene, hexane and heptane; chlorinated solvents suchas methylene chloride, chloroform and dichloroethane; ethers such asdiethyl ether, tetrahydrofuran, and dibutyl ether; ketones such asacetone and 2-butanone; esters such as ethyl acetate and butyl acetate;nitriles such as acetonitrile; alcohols such as methanol and ethanol;aprotic polar solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, and dimethyl sulfoxide; and water, which may beused alone or in admixture. To the reaction, a phase transfer catalystsuch as tetrabutylammonium hydrogensulfate may be added. The amount ofphase transfer catalyst added is preferably 0.0001 to 1.0 mole, and morepreferably 0.001 to 0.5 mole per mole of the reactant, halo-estercompound (9). Less than 0.0001 mole of the catalyst may fail to achievethe catalytic effect whereas more than 1.0 mole of the catalyst may beuneconomical due to increased material costs.

The temperature of esterifying reaction is preferably in the range of−70° C. to the boiling point of the solvent used. An appropriatetemperature may be selected in accordance with other reactionconditions, although it is most often in the range of 0° C. to theboiling point of the solvent used. Since noticeable side reactions occurat higher temperatures, it is important for gaining higher yields thatthe reaction run at a temperature which is low, but enough to ensure apractically acceptable reaction rate. Also for higher yields, thereaction time is preferably determined by monitoring the reactionprocess by thin-layer chromatography (TLC) or gas chromatography (GC).Usually the reaction time is about 30 minutes to about 40 hours. Thedesired fluorinated monomer (1) may be obtained from the reactionmixture by ordinary aqueous work-up. If necessary, the compound may bepurified by standard techniques like distillation, recrystallization andchromatography.

Additive Polymer

A second embodiment provides a polymer useful as an additive to a resistcomposition, and specifically a polymer or high-molecular-weightcompound comprising recurring units represented by the general formula(1a). For convenience of description, the polymer comprising recurringunits of formula (1a) is referred as “polymer P1,” hereinafter.

Herein R¹ to R⁶, A and k¹ are as defined above.

Polymer P1 is characterized in that the recurring units of formula (1a)each contain a plurality of fluorine atoms. Once polymer P1 is added toa resist composition, polymer P1 itself functions as a surfactant toprovide a distribution at the time when a resist film is formed, thatpolymer P1 is segregated at the resist film surface.

In general, fluorinated polymers exert excellent functions of waterrepellency and water slip. When polymer P1 is used as a resist additive,it is possible to form a resist film having a surface exerting excellentwater repellency and water slip at the same time as its formation. Aneffect equivalent to the use of resist protective coating material isexpectable. This approach is also advantageous in cost because iteliminates the steps of forming and removing a resist protectivecoating.

Since the recurring unit of formula (1a) contains a fluorinated estersusceptible to alkaline hydrolysis, the unit is readily hydrolyzed inalkaline developer to create a carboxylic acid unit (1aa) as illustratedin the reaction scheme below. Then, when polymer P1 is used as a resistadditive, the surface of a resist film after alkaline developmentbecomes more hydrophilic and the surface contact angle thereof issignificantly reduced. As a result, the occurrence of blob defects maybe inhibited.

Herein R¹ to R⁶, A and k¹ are as defined above.

Polymer P1 may be further improved in water repellency, water slip,alkaline dissolution, and contact angle after development, byincorporating recurring units of one or more type selected from thegeneral formulae (2a) to (2i) in addition to the recurring units offormula (1a).

Herein R¹ is as defined above. R^(4a) and R^(4b) each are hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, orR^(4a) and R^(4b) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon atom to which they are attached. R^(5a)is hydrogen, a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon or fluorinated hydrocarbon group, or an acid labile group,and in the case of hydrocarbon group, any constituent moiety —CH₂— maybe replaced by —O— or —C(′O)—. R^(6a), R^(6b) and R^(6c) each arehydrogen, or a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon group, a pair of R^(6a) and R^(6b), R^(6a) and R^(6c), orR^(6b) and R^(6c) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon atom to which they are attached. R^(7a)is hydrogen, or a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon group, R^(7b) is a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, a pair of R^(7a) and R^(7b) may bondtogether to form a non-aromatic ring of 3 to 8 carbon atoms with thecarbon and oxygen atoms to which they are attached. R^(8a) is astraight, branched or cyclic C₁-C₁₅ monovalent fluorinated hydrocarbongroup. R^(9a) is a straight, branched or cyclic C₁-C₁₀ monovalentfluorinated hydrocarbon group. R^(10a) is a straight, branched or cyclicC₁-C₁₅ monovalent hydrocarbon group which may contain halogen or oxygen.Subscript k² is 0 or 1.

In formulae (2a) to (2i), the straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon groups represented by R^(4a), R^(4b), R^(5a),R^(6a), R^(6b), R^(6c), R^(7a), and R^(7b) are preferably alkyl groups,examples of which include methyl, ethyl, n-propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl,cyclohexylbutyl, and adamantyl. A pair of R^(4a) and R^(4b), R^(6a) andR^(6b), R^(6a) and R^(6c), R^(6b) and R^(6c), or R^(7a) and R^(7b) maybond together to form a non-aromatic ring of 3 to 8 carbon atoms withthe carbon atom (or carbon and oxygen atoms) to which they are attached.In this case, these groups each are an alkylene group, examples of whichare the foregoing alkyl groups with one hydrogen atom eliminated, andexemplary rings include cyclopentyl and cyclohexyl.

The straight, branched or cyclic C₁-C₁₅ monovalent fluorinatedhydrocarbon groups represented by R^(5a) and R^(8a) are preferablyfluoroalkyl groups, which are typically the foregoing alkyl groups inwhich some or all hydrogen atoms are substituted by fluorine atoms.Examples include trifluoromethyl, 2,2,2-trifluoroethyl,3,3,3-trifluoro-1-propyl, 3,3,3-trifluoro-2-propyl,2,2,3,3-tetrafluoropropyl, 1,1,1,3,3,3-hexafluoroisopropyl,2,2,3,3,4,4,4-heptafluorobutyl, 2,2,3,3,4,4,5,5-octafluoropentyl,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, 2-(perfluorobutyl)ethyl,2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl,2-(perfluorodecyl)ethyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl. Thestraight, branched or cyclic C₁-C₁₀ monovalent fluorinated hydrocarbongroups represented by R^(9a) are also preferably fluoroalkyl groups,examples of which include trifluoromethyl, 2,2,2-trifluoroethyl,3,3,3-trifluoro-1-propyl, 3,3,3-trifluoro-2-propyl,2,2,3,3-tetrafluoropropyl, 1,1,1,3,3,3-hexafluoroisopropyl,2,2,3,3,4,4,4-heptafluorobutyl, 2,2,3,3,4,4,5,5-octafluoropentyl,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, 2-(perfluorobutyl)ethyl,2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl, and3,3,4,4,5,5,6,6,6-nonafluorohexyl.

The acid labile group represented by R^(5a) may be selected from avariety of such groups. Examples of the acid labile group are groups ofthe following general formulae (L1) to (L4), tertiary alkyl groups of 4to 20 carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilylgroups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkylgroups of 4 to 20 carbon atoms.

Herein R^(L01) and R^(L02) are hydrogen or straight, branched or cyclicalkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms.R^(L03) is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may contain a heteroatom such asoxygen, examples of which include unsubstituted straight, branched orcyclic alkyl groups and substituted forms of such alkyl groups in whichsome hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino,alkylamino or the like. R^(L04) is a tertiary alkyl group of 4 to 20carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group inwhich each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4to 20 carbon atoms, or a group of formula (L1). R^(L05) is an optionallysubstituted, straight, branched or cyclic C₁-C₁₀ alkyl group or anoptionally substituted C₆-C₂₀ aryl group. R^(L06) is an optionallysubstituted, straight, branched or cyclic C₁-C₁₀ alkyl group or anoptionally substituted C₆-C₂₀ aryl group. R^(L07) to R^(L16)independently represent hydrogen or an optionally substituted monovalenthydrocarbon group of 1 to 15 carbon atoms. Letter y is an integer of 0to 6, m is equal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n isequal to 2 or 3. The broken line denotes a valence bond.

In formula (L1), exemplary groups of R^(L01) and R^(L02) include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, n-octyl, and adamantyl. R^(L03) is amonovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms, which may contain a heteroatom such as oxygen, examples ofwhich include unsubstituted straight, branched or cyclic alkyl groupsand substituted forms of such alkyl groups in which some hydrogen atomsare replaced by hydroxyl, alkoxy, oxo, amino, alkylamino or the like.Illustrative examples of the straight, branched or cyclic alkyl groupsare as exemplified above for R^(L01) and R^(L02), and examples of thesubstituted alkyl groups are as shown below.

A pair of R^(L01) and R^(L02), or R^(L01) and R^(L03), or R^(L02) andR^(L03) may bond together to form a ring with carbon and oxygen atoms towhich they are attached. Each of ring-forming R^(L01), R^(L02) andR^(L03) is a straight or branched alkylene group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms when they form a ring.

In formula (L2), exemplary tertiary alkyl groups of R^(L04) aretert-butyl, tert-amyl, 1,1-diethylpropyl, 2-cyclopentylpropan-2-yl,2-cyclohexylpropan-2-yl, 2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl,2-(adamantan-1-yl)propan-2-yl, 1-ethylcyclopentyl, 1-butylcyclopentyl,1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl,1-ethyl-2-cyclohexenyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, andthe like. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl.

In formula (L3), examples of the optionally substituted alkyl groups ofR^(L05) include straight, branched or cyclic alkyl groups such asmethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, andbicyclo[2.2.1]heptyl, and substituted forms of such groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxy,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio,sulfo or other radicals or in which a methylene moiety is replaced byoxygen or sulfur. Examples of optionally substituted C₆-C₂₀ aryl groupsinclude phenyl, methylphenyl, naphthyl, anthryl, phenanthryl, andpyrenyl.

In formula (L4), examples of optionally substituted, straight, branchedor cyclic C₁-C₁₀ alkyl groups and optionally substituted C₆-C₂₀ arylgroups of R^(L06) are the same as exemplified for R^(L05). ExemplaryC₁-C₁₅ monovalent hydrocarbon groups of R^(L07) to R^(L16) are straight,branched or cyclic alkyl groups such as methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyland cyclohexylbutyl, and substituted forms of these groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxy,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio,sulfo or other radicals. Alternatively, two of R^(L07) to R^(L16) maybond together to form a ring with the carbon atom(s) to which they areattached (for example, a pair of R^(L07) and R^(L08), R^(L07) andR^(L09), and R^(L10), R^(L09) and R^(L10), R^(L11) and R^(L12), pR^(L13) and R^(L14), or a similar pair form a ring). Each of R^(L07) toR^(L16) represents a divalent C₁-C₁₅ hydrocarbon group (typicallyalkylene) when they form a ring, examples of which are those exemplifiedabove for the monovalent hydrocarbon groups, with one hydrogen atombeing eliminated. Two of R^(L07) to R^(L16) which are attached tovicinal carbon atoms may bond together directly to form a double bond(for example, a pair of R^(L07) and R^(L09), R^(L09) and R^(L15),R^(L13) and R^(L15), or a similar pair).

Of the acid labile groups of formula (L1), the straight and branchedones are exemplified by the following groups.

Of the acid labile groups of formula (L1), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Examples of the acid labile groups of formula (L2) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Examples of the acid labile groups of formula (L3) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-cyclohexylcyclopentyl, 1-(4-methoxy-n-butyl)cyclopentyl,1-(bicyclo[2.2.1]heptan-2-yl)cyclopentyl,1-(7-oxabicyclo[2.2.1]heptan-2-yl)cyclopentyl, 1-methylcyclohexyl,1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

Of the acid labile groups of formula (L4), those groups of the followingformulae (L4-1) to (L4-4) are preferred.

In formulas (L4-1) to (L4-4), the broken line denotes a bonding site anddirection. R^(L41) is each independently a monovalent hydrocarbon group,typically a straight, branched or cyclic C₁-C₁₀ alkyl group, such asmethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-amyl, n-pentyl, n-hexyl, cyclopentyl and cyclohexyl.

For formulas (L4-1) to (L4-4), there can exist enantiomers anddiastereomers. Each of formulae (L4-1) to (L4-4) collectively representsall such stereoisomers. Such stereoisomers may be used alone or inadmixture.

For example, the general formula (L4-3) represents one or a mixture oftwo selected from groups having the following general formulas (L4-3-1)and (L4-3-2).

Note that R^(L41) is as defined above.

Similarly, the general formula (L4-4) represents one or a mixture of twoor more selected from groups having the following general formulas(L4-4-1) to (L4-4-4).

Note that R^(L41) is as defined above.

Each of formulas (L4-1) to (L4-4), (L4-3-1) and (L4-3-2), and (L4-4-1)to (L4-4-4) collectively represents an enantiomer thereof and a mixtureof enantiomers.

It is noted that in the above formulas (L4-1) to (L4-4), (L4-3-1) and(L4-3-2), and (L4-4-1) to (L4-4-4), the bond direction is on the exoside relative to the bicyclo[2.2.1]heptane ring, which ensures highreactivity for acid catalyzed elimination reaction (see JP-A2000-336121). In preparing these monomers having a tertiary exo-alkylgroup of bicyclo[2.2.1]heptane structure as a substituent group, theremay be contained monomers substituted with an endo-alkyl group asrepresented by the following formulas (L4-1-endo) to (L4-4-endo). Forgood reactivity, an exo proportion of at least 50 mol % is preferred,with an exo proportion of at least 80 mol % being more preferred.

Note that R^(L14) is as defined above.

Illustrative examples of the acid labile group of formula (L4) are givenbelow.

Examples of the tertiary C₄-C₂₀ alkyl groups, trialkylsilyl groups inwhich each alkyl moiety has 1 to 6 carbon atoms, and C₄-C₂₀ oxoalkylgroups, represented by R^(5a), are as exemplified for R^(L04) and thelike.

Illustrative examples of the recurring units of formulae (2a) to (2i)are given below, but not limited thereto.

Herein R¹ is as defined above.

Although polymer P1 comprising recurring units of formula (1a) incombination with recurring units of formulae (2a) to (21) exertssatisfactory performance, recurring units of one or more types selectedfrom formulae (3a) to (3e), (4a) to (4e), (5a) to (5c), and (6a) to (6c)may be further incorporated therein for the purposes of impartingfurther water repellency and water slip, and controlling alkalinesolubility and developer affinity.

Herein R¹⁵ is a C₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbongroup, R¹⁶ is an adhesive group, R¹⁷ is an acid labile group, R¹⁸ is asingle bond or a C₁-C₁₅ divalent organic group, typically alkylene, andR¹⁹ and R²⁰⁶ each are hydrogen, methyl or trifluoromethyl.

Examples of the C₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbongroup represented by R¹⁵ are the same as illustrated for R^(5a) andR^(8a).

The adhesive group represented by R¹⁶ may be selected from a variety ofsuch groups, typically those groups shown below.

Herein, the broken line designates a valence bond.

The acid labile group represented by R¹⁷ may be selected from thosegroups illustrated for R^(15a).

Suitable C₁-C₁₅ divalent organic groups represented by R¹⁸ include theabove-illustrated monovalent hydrocarbon groups with one hydrogen atomeliminated (e.g., methylene and ethylene) and groups of the followingformulae.

Herein, the broken line designates a valence bond.Polymer Synthesis

The polymer P1 used herein may be synthesized by general polymerizationprocesses including radical polymerization using initiators such as2,2′-azobisisobutyronitrile (AIBN), and ionic (or anionic)polymerization using alkyllithium or the like. The polymerization may becarried out by a standard technique. Preferably polymer P1 is preparedby radical polymerization while the polymerization conditions may bedetermined in accordance with the type and amount of initiator,temperature, pressure, concentration, solvent, additives, and the like.

Examples of the radical polymerization initiator used herein include azocompounds such as 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2,4,4-trimethylpentane), and dimethyl2,2′-azobis(isobutyrate); peroxides such as tert-butylperoxypivalate,lauroyl peroxide, benzoyl peroxide, and tert-butylperoxylaurate;water-soluble polymerization initiators such as potassium persulfate;and redox initiators comprising a peroxide (e.g., potassium persulfateor hydrogen peroxide) combined with a reducing agent (e.g., sodiumsulfite). Although the amount of polymerization initiator used may varywith its type and other polymerization conditions, it is generally usedin an amount of 0.001 to 10 mol %, and preferably 0.01 to 6 mol % basedon the total moles of monomers to be polymerized.

During the synthesis of polymer P1, any known chain transfer agent suchas dodecyl mercaptan or 2-mercaptoethanol may be added for molecularweight control purpose. The amount of chain transfer agent added ispreferably 0.01 to 10 mol % based on the total moles of monomers to bepolymerized.

Polymer P1 may be synthesized by combining suitable monomers selectedfrom polymerizable monomers corresponding to recurring units of formulae(1a), (2a) to (2i), (3a) to (3e), (4a) to (4e), (5a) to (5c), and (6a)to (6c), adding an initiator and chain transfer agent to the monomermixture, and effecting polymerization.

In polymer P1 wherein U1 stands for a total molar number of a monomer ormonomers corresponding to units of formula (1a), U2 stands for a totalmolar number of a monomer or monomers corresponding to units of formulae(2a) to (2i), and U3 stands for a total molar number of a monomer ormonomers corresponding to units of formulae (3a) to (3e), (4a) to (4e),(5a) to (5c), and (6a) to (6c), with the proviso that U1+U2+U3=U (=100mol %), values of U1, U2, and U3 are preferably determined so as tomeet:

0<U1/U<1, more preferably 0.1≦U1/U≦0.8, even more preferably0.1≦U1/U≦0.7,

0≦U2/U<1, more preferably 0.1≦U2/U≦0.8, even more preferably0.2≦U2/U≦0.8, and

0≦U3/U<1, more preferably 0≦U3/U≦0.4, even more preferably 0≦U3/U≦0.2.

In conducting polymerization, a solvent may be used if necessary. Anysolvent may be used as long as it does not interfere with the desiredpolymerization reaction. Typical solvents used herein include esterssuch as ethyl acetate, n-butyl acetate, and γ-butyrolactone; ketonessuch as acetone, methyl ethyl ketone, and methyl isobutyl ketone;aliphatic or aromatic hydrocarbons such as toluene, xylene andcyclohexane; alcohols such as isopropyl alcohol and ethylene glycolmonomethyl ether; and ether solvents such as diethyl ether, dioxane, andtetrahydrofuran, which may be used alone or in admixture. Although theamount of solvent used may vary with the desired degree ofpolymerization (or molecular weight), the amount of initiator added, andother polymerization conditions such as polymerization temperature, itis generally used in such an amount as to provide a concentration of 0.1to 95% by weight, preferably 5 to 90% by weight of monomers to bepolymerized.

Although the temperature of the polymerization reaction may vary withthe identity of polymerization initiator or the boiling point ofsolvent, it is preferably in the range of 20 to 200° C., and morepreferably 50 to 140° C. Any desired reactor or vessel may be used forthe polymerization reaction.

From the solution or dispersion of the polymer thus synthesized, theorganic solvent or water serving as the reaction medium is removed byany well-known techniques. Suitable techniques include, for example,re-precipitation followed by filtration, and heat distillation undervacuum.

Desirably polymer P1 has a weight average molecular weight (Mw) of 1,000to 500,000, and especially 2,000 to 30,000, as determined intetrahydrofuran solvent by gel permeation chromatography (GPC) usingpolystyrene standards. This is because a polymer with too low a Mw maybe dissolvable in water whereas too high a Mw may lead to a decline ofalkali solubility or cause coating defectives during spin coating.

In polymer P1, R^(5a) in formula (2a), (2b) and (2f) and R¹⁷ in formula(3c) and (4c) may be introduced by post-protection reaction.Specifically, a polymer may be synthesized by polymerizing a monomerwherein R^(5a) and R¹⁷ are hydrogen to synthesize an intermediatepolymer, then effecting post-protection reaction to substitute R^(5a)and R¹⁷ for some or all hydroxyl groups in the intermediate polymer.

Herein R^(5a) and R¹⁷ are as defined above, and X is chlorine, bromineor iodine.

The desired (post-protected) polymer is obtainable throughpost-protection reaction by reacting the intermediate polymer with abase in an amount of 1 to 2 equivalents relative to the desired degreeof substitution of hydroxyl groups, and then with R^(5a)—X or R¹⁷—X inan amount of 1 to 2 equivalents relative to the base.

The post-protection reaction may be effected in a solvent, which isselected from hydrocarbons such as benzene and toluene, and ethers suchas dibutyl ether, diethylene glycol diethyl ether, diethylene glycoldimethyl ether, tetrahydrofuran and 1,4-dioxane, alone or in admixture.Suitable bases used herein include, but are not limited to, sodiumhydride, n-butyllithium, lithium diisopropylamide, triethylamine, andpyridine.

Resist Composition

When polymer P1 is added to a resist composition, a total amount ofpolymer(s) P1 is preferably 0.1 to 50 parts, and more preferably 0.5 to10 parts by weight per 100 parts by weight of a base resin (B). At least0.1 part of polymer P1 is effective for improving the receding contactangle with water of a resist film at its surface. When the amount ofpolymer P1 is up to 50 parts, a resist film has a sufficiently low rateof dissolution in alkaline developer to maintain the height of aresultant fine size pattern.

In the resist composition of the invention, polymer P1 is used inadmixture with a base resin (B) to be described below. Since polymer P1contains a plurality of fluorine atoms, overall polymer P1 functions asa surfactant so that it may segregate in an upper layer of a resist filmbeing spin coated. The resulting resist film displays improved waterrepellency and water slip on its surface and prevents water-solublecomponents from being leached out of the resist material. Also, polymerP1 which contains an alkaline hydrolysis-susceptible structure asmentioned above may enhance the hydrophilic property of the resist filmsurface after development, inhibiting the occurrence of blob defects.

The resist composition contains (B) a base resin or polymer having alactone ring-derived structure and/or hydroxyl group-containingstructure and/or maleic anhydride-derived structure which becomessoluble in alkaline developer under the action of acid. The polymerswhich can serve as the base resin (B) include (meth)acrylate polymers,(α-trifluoromethyl)acrylate-maleic anhydride copolymers,cycloolefin-maleic anhydride copolymers, polynorbornene, cycloolefinring-opening metathesis polymerization (ROMP) polymers, hydrogenatedcycloolefin ROMP polymers, polyhydroxystyrene, copolymers ofhydroxystyrene with one or more of (meth)acrylate, styrene,vinylnaphthalene, vinylanthracene, vinylpyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, indene, hydroxyindene, acenaphthylene, andnorbornadiene derivatives, and novolac resins. Suitable polymerspossessing a lactone ring-derived structure and/or hydroxylgroup-containing structure and/or maleic anhydride-derived structure andhaving an acid labile group so that the polymer may become soluble inalkaline developer under the action of acid are described in U.S. Pat.No. 7,537,880 or JP-A 2008-111103, paragraphs [0072] to [0120]. Thepolymer serving as base resin (B) is not limited to one type and amixture of two or more polymers may be added. The use of plural polymersallows for easy adjustment of resist properties.

The base resin (B) may comprise recurring units of at least one typeselected from the general formulae (2A) to (2D).

Herein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA is anacid labile group, XB and XC are each independently a single bond or astraight or branched C₁-C₄ divalent hydrocarbon group (typicallyalkylene), YA is a substituent group having a lactone structure, ZA ishydrogen, or a C₁-C₁₅ fluoroalkyl group or C₁-C₁₅fluoroalcohol-containing substituent group, and k^(1A) is an integer of1 to 3.

A polymer comprising recurring units of formula (2A) is decomposed underthe action of an acid to generate carboxylic acid so that the polymermay become alkali soluble. While the acid labile group XA may beselected from a variety of such groups, it may be as exemplified abovefor R^(5a) in formulae (2a) to (2i).

Examples of recurring units of formula (2A) are given below, but notlimited thereto.

Examples of recurring units of formula (2B) are given below, but notlimited thereto.

Examples of recurring units of formula (2C) are given below, but notlimited thereto.

Examples of recurring units of formula (2D) are given below, but notlimited thereto.

In order that the resist composition function as a chemically amplifiedpositive resist composition, (C) a compound capable of generating anacid upon exposure to high-energy radiation, referred to as “photoacidgenerator” or PAG, may be compounded. The PAG may be any compoundcapable of generating an acid upon exposure of high-energy radiation.Suitable PAGs include sulfonium salts, iodonium salts,sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acidgenerators. Exemplary acid generators are described in JP-A 2010-002599,paragraphs [0091] to [0117].

The preferred PAGs are those compounds of the general formula (C)-1.

Herein R⁴⁰⁵, R⁴⁰⁶, and R⁴⁰⁷ are each independently hydrogen or astraight, branched or cyclic C₁-C₂₀ monovalent hydrocarbon group whichmay contain a heteroatom, typically an alkyl or alkoxy group. R⁴⁰⁸ is astraight, branched or cyclic C₇-C₃₀ monovalent hydrocarbon group whichmay contain a heteroatom.

Examples of the hydrocarbon groups optionally containing a heteroatom,represented by R⁴⁰⁵, R⁴⁰⁶, and R⁴⁰⁷, include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl,ethylcyclohexyl, butylcyclohexyl, adamantyl, ethyladamantyl,butyladamantyl, and modified forms of the foregoing in which anycarbon-carbon bond is separated by a hetero-atomic grouping such as —O—,—S—, —SO—, —SO₂—, —NH—, —C(═O)—, —C(═O)O—, or —C(═O)NH—, or any hydrogenatom is replaced by a functional radical such as —OH, —NH₂, —CHO, or—CO₂H. Examples of the straight, branched or cyclic C₇-C₃₀ monovalenthydrocarbon groups optionally containing a heteroatom, represented byR⁴⁰⁸, are shown below, but not limited thereto.

Illustrative examples of acid generators (C)-1 are shown below, but notlimited thereto.

It is noted that an acid diffusion controlling function may be providedwhen two or more PAGs are used in admixture provided that one PAG is anonium salt capable of generating a weak acid. Specifically, in a systemusing a mixture of a PAG capable of generating a strong acid (e.g.,fluorinated sulfonic acid) and an onium salt capable of generating aweak acid (e.g., non-fluorinated sulfonic acid or carboxylic acid), ifthe strong acid generated from the PAG upon exposure to high-energyradiation collides with the unreacted onium salt having a weak acidanion, then a salt exchange occurs whereby the weak acid is released andan onium salt having a strong acid anion is formed. In this course, thestrong acid is exchanged into the weak acid having a low catalysis,incurring apparent deactivation of the acid for enabling to control aciddiffusion.

If the PAG capable of generating a strong acid is also an onium salt, anexchange from the strong acid (generated upon exposure to high-energyradiation) to a weak acid as above can take place, but it never happensthat the weak acid (generated upon exposure to high-energy radiation)collides with the unreacted onium salt capable of generating a strongacid to induce a salt exchange. This is because of a likelihood of anonium cation forming an ion pair with a stronger acid anion.

An amount of the PAG added as component (C) is not particularly limitedas long as the objects of the invention are not compromised. The amountof PAG is 0.1 to 20 parts, more preferably 0.1 to 10 parts, and mostpreferably 0.1 to 5 parts by weight per 100 parts by weight of the baseresin in the composition. An excess of the PAG may cause some problemssuch as degraded resolution and foreign particles left afterdevelopment/resist film stripping. The PAG may be used alone or inadmixture of two or more. The transmittance of the resist film can becontrolled by using a PAG having a low transmittance at the exposurewavelength and adjusting the amount of the PAG added. As long as PAG isup to 20 phr, the resulting photoresist film has a fully hightransmittance and a minimal likelihood of degraded resolution. The PAGmay be used alone or in admixture of two or more. The transmittance ofthe resist film can be controlled by using a PAG having a lowtransmittance at the exposure wavelength and adjusting the amount of thePAG added.

The resist composition may further comprise one or more of (D) anorganic solvent, (E) a basic compound, (F) a dissolution regulator, (G)a surfactant, and (H) an acetylene alcohol derivative.

The organic solvent (D) used herein may be any organic solvent in whichpolymer P1, the base resin, PAG, and other components are soluble.Exemplary solvents are described in JP-A 2008-111103, paragraph [0144].The organic solvents may be used alone or in combinations of two or morethereof. An appropriate amount of the organic solvent used is 200 to3,000 parts, especially 400 to 2,500 parts by weight per 100 parts byweight of the base resin (B). It is recommended to use diethylene glycoldimethyl ether, 1-ethoxy-2-propanol, propylene glycol monomethyl etheracetate (PGMEA), and mixtures thereof because the acid generator is mostsoluble therein.

As the basic compound (E), nitrogen-containing organic compounds arepreferred and may be used alone or in admixture. Those compounds capableof suppressing the rate of diffusion when the acid generated by the acidgenerator diffuses within the resist film are useful. The inclusion ofnitrogen-containing organic compound holds down the rate of aciddiffusion within the resist film, resulting in better resolution. Inaddition, it suppresses changes in sensitivity following exposure andreduces substrate and environment dependence, as well as improving theexposure latitude and the pattern profile.

Suitable nitrogen-containing organic compounds include primary,secondary, and tertiary aliphatic amines, mixed amines, aromatic amines,heterocyclic amines, nitrogen-containing compounds having carboxylgroup, nitrogen-containing compounds having sulfonyl group,nitrogen-containing compounds having hydroxyl group, nitrogen-containingcompounds having hydroxyphenyl group, amide, imide and carbamatederivatives. Illustrative examples are described in JP-A 2008-111103,paragraphs [0149] to [0163]. The basic compound is preferably used in anamount of 0.001 to 2 parts, more preferably 0.01 to 1 part by weight per100 parts by weight of the base resin (B). At least 0.001 phr achievesthe desired addition effect whereas up to 2 phr minimizes the risk ofreducing sensitivity.

The dissolution regulator or inhibitor (F) which can be added to theresist composition is a compound having on the molecule at least twophenolic hydroxyl groups which are protected with an acid labile group,or a compound having on the molecule at least one carboxyl group whichis protected with an acid labile group. Exemplary regulators aredescribed in JP-A 2008-122932, paragraphs [0155] to [0178].

Optionally, the resist composition of the invention may further comprise(G) a surfactant which is commonly used for facilitating the coatingoperation. The surfactant may be added in conventional amounts so longas this does not compromise the objects of the invention.

Illustrative, non-limiting examples of the surfactant (G) includenonionic surfactants, for example, polyoxyethylene alkyl ethers such aspolyoxyethylene lauryl ether, polyoxyethylene stearyl ether,polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether,polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenolether and polyoxyethylene nonylphenol ether, polyoxyethylenepolyoxypropylene block copolymers, sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate,and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylenesorbitan monolaurate, polyoxyethylene sorbitan monopalmitate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitantrioleate, and polyoxyethylene sorbitan tristearate; fluorochemicalsurfactants such as EFTOP EF301, EF303 and EF352 (JEMCO Inc.), MegafaceF171, F172, F173, R08, R30, R90 and R94 (DIC Corp.), Fluorad FC-430,FC-431, FC-4430 and FC-4432 (Sumitomo 3M Co., Ltd.), Asahiguard AG710,Surflon S-381, S-382, S-386, SC101, SC102, SC103, SC104, SC105, SC106,KH-10, KH-20, KH-30 and KH-40 (Asahi Glass Co., Ltd.), and SurfynolE1004 (Nissin Chemical Industry Co., Ltd.); organosiloxane polymersKP341, X-70-092 and X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylicacid or methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha UshiKagaku Kogyo Co., Ltd.). Additional useful surfactants include partiallyfluorinated oxetane ring-opened polymers having the structural formula(surf-1) below.

It is provided herein that R, Rf, A, B, C, m′, and n′ are applied toonly formula (surf-1), independent of their descriptions other than forthe surfactant. R is a di- to tetra-valent C₂-C₅ aliphatic group.Exemplary divalent groups include ethylene, 1,4-butylene, 1,2-propylene,2,2-dimethyl-1,3-propylene and 1,5-pentylene. Exemplary tri- andtetra-valent groups are shown below.

Herein the broken line denotes a valence bond. These formulae arepartial structures derived from glycerol, trimethylol ethane,trimethylol propane, and pentaerythritol, respectively. Of these,1,4-butylene and 2,2-dimethyl-1,3-propylene are preferably used.

Rf is trifluoromethyl or pentafluoroethyl, and preferablytrifluoromethyl. The letter m′ is an integer of 0 to 3, n′ is an integerof 1 to 4, and the sum of m′ and n′, which represents the valence of R,is an integer of 2 to 4. A is equal to 1, B is an integer of 2 to 25,and C is an integer of 0 to 10. Preferably, B is an integer of 4 to 20,and C is 0 or 1. Note that the above structural formula does notprescribe the arrangement of respective constituent units while they maybe arranged either in blocks or randomly. For the preparation ofsurfactants in the form of partially fluorinated oxetane ring-openedpolymers, reference should be made to U.S. Pat. No. 5,650,483, forexample.

Of the foregoing surfactants, FC-4430, Surflon S-381, Surfynol E1004,KH-20, KH-30, and oxetane ring-opened polymers of formula (surf-1) arepreferred. These surfactants may be used alone or in admixture.

In the resist composition, the surfactant is preferably compounded in anamount of up to 2 parts, and especially up to 1 part by weight, per 100parts by weight of the base resin. The amount of the surfactant, ifadded, is preferably at least 0.01 phr.

Optionally, the resist composition may further comprise (H) an acetylenealcohol derivative. Exemplary compounds are described in JP-A2008-122932, paragraphs [0180] to [0181].

Optionally, the resist composition may further comprise (I) afluorinated alcohol. When the resist composition contains (E) a basiccompound, the fluorinated ester in recurring units (la) of polymer P1 issubject to gradual hydrolysis during storage, which may lead to adecline of water repellent and water slip performance during theimmersion lithography process. In such a case, (I) a fluorinated alcoholmay be added to the resist composition for suppressing the hydrolysiswhich is otherwise promoted by the basic compound (E), thus enhancingstorage stability.

Examples of the fluorinated alcohol include, but are not limited to,2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol,1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol,1,1,1,3,3,3-hexafluoro-2-trifluoromethyl-2-propanol,2,2,3,4,4,4-hexafluoro-1-butanol, 2,2,2,2′,2′,2′-hexafluorocumylalcohol,and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol.

The fluorinated alcohol (I) is preferably used in an amount of 0.01 to10 parts, more preferably 0.01 to 5 parts by weight per part by weightof the basic compound (E).

Pattern Forming Process

It is now described how to form a pattern using the resist compositionof the invention. A pattern may be formed from the resist compositionusing any well-known lithography process. The preferred process includesat least the steps of forming a resist coating on a substrate, exposingit to high-energy radiation, and developing it with a developer.

The resist composition is applied onto a substrate, typically a siliconwafer by a suitable coating technique such as spin coating. The coatingis prebaked on a hot plate at a temperature of 60 to 150° C. for 1 to 10minutes, preferably 80 to 140° C. for 1 to 5 minutes, to form a resistfilm of 0.01 to 2.0 μm thick. It is noted in conjunction with spincoating that if the resist composition is coated onto the surface of asubstrate which has been wetted with the resist solvent or a solutionmiscible with the resist solvent, then the amount of the resistcomposition dispensed can be reduced (see JP-A H09-246173).

A mask having the desired pattern is then placed over the photoresistfilm, and the film exposed through the mask to an electron beam or tohigh-energy radiation such as deep-UV, excimer laser or x-ray in a doseof 1 to 200 mJ/cm², and preferably 10 to 100 mJ/cm². The high-energyradiation used herein preferably has a wavelength in the range of 180 to250 nm.

Light exposure may be dry exposure in air or nitrogen atmosphere, orimmersion lithography of providing a liquid, typically water between theresist film and the projection lens. The liquid used for immersion is aliquid having a refractive index of at least 1 and high transparency atthe exposure wavelength, such as water or alkane. EB or EUV exposure invacuum is also acceptable.

The resist film formed from the resist composition has such barrierproperties to water that it may inhibit resist components from beingleached out in water and as a consequence, eliminate a need for aprotective coating in the immersion lithography and reduce the costassociated with protective coating formation or the like. The resistfilm has so high a receding contact angle with water that few liquiddroplets may be left on the surface of the photoresist film afterimmersion lithography scanning, minimizing pattern formation failuresinduced by liquid droplets left on the film surface.

In another version of immersion lithography, a protective coating may beformed on top of the resist film. The resist protective coating may beeither of the solvent stripping type or of the developer dissolutiontype. A resist protective coating of the developer dissolution type isadvantageous for process simplicity because it can be stripped duringdevelopment of a resist film of the resist composition. The resistprotective coating used in the immersion lithography may be formed froma coating solution, for example, a topcoat solution of a polymer havingacidic units such as 1,1,1,3,3,3-hexafluoro-2-propanol, carboxyl orsulfo groups which is insoluble in water and soluble in an alkalinedeveloper liquid, in a solvent selected from alcohols of at least 4carbon atoms, ethers of 8 to 12 carbon atoms, and mixtures thereof. Theresist protective coating is not limited thereto.

The resist protective coating may be formed by spin coating a topcoatsolution onto a prebaked resist film, and prebaking on a hot plate at 50to 150° C. for 1 to 10 minutes, preferably at 70 to 140° C. for 1 to 5minutes. Preferably the protective coating has a thickness in the rangeof 10 to 500 nm. As in the case of resist compositions, the amount ofthe protective coating material dispensed in forming a protectivecoating by spin coating may be reduced by previously wetting the resistfilm surface with a suitable solvent and applying the protective coatingmaterial thereto.

After exposure to high-energy radiation through a photomask, the resistfilm is post-exposure baked (PEB) on a hot plate at 60 to 150° C. for 1to 5 minutes, and preferably at 80 to 140° C. for 1 to 3 minutes.

Where a resist protective coating is used, sometimes water is left onthe protective coating prior to PEB. If PEB is performed in the presenceof residual water, water can penetrate through the protective coating tosuck up the acid in the resist during PEB, impeding pattern formation.To fully remove the water on the protective coating prior to PEB, thewater on the protective coating should be dried or recovered by suitablemeans, for example, spin drying, purging the protective coating surfacewith dry air or nitrogen, or optimizing the shape of a water recoverynozzle on the relevant stage or a water recovery process.

After the exposure, development is carried out by a conventional methodsuch as dip, puddle, or spray development with an aqueous alkalinesolution such as tetramethylammonium hydroxide (TMAH) solution. Thedeveloper may have a concentration of 0.1 to 5 wt %, preferably 2 to 3wt %. A typical developer is a 2.38 wt % TMAH aqueous solution. Thedevelopment time is 10 to 300 seconds, and preferably 0.5 to 2 minutes.These steps result in the formation of the desired pattern on thesubstrate.

Where polymer P1 is used as an additive to a resist material for usewith mask blanks, a resist solution is prepared by adding polymer P1 toa base resin and dissolving them in an organic solvent. The resistsolution is coated on a mask blank substrate of SiO₂, Cr, CrO, CrN, MoSior the like. A SOG film and an organic undercoat film may intervenebetween the resist film and the blank substrate to construct athree-layer structure which is also acceptable herein.

As the base resin of the resist composition for use with mask blanks,novolac resins and hydroxystyrene are often used. Those resins in whichalkali soluble hydroxyl groups are substituted by acid labile groups areused for positive resists while these resins in combination withcrosslinking agents are used for negative resists. Base polymers whichcan be used herein include copolymers of hydroxystyrene with one or moreof (meth)acrylic derivatives, styrene, vinylnaphthalene,vinylanthracene, vinylpyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, indene, hydroxyindene, acenaphthylene, andnorbornadiene derivatives.

Once the resist coating is formed, the structure is exposed to EB invacuum using an EB image-writing system. The exposure is followed bypost-exposure baking (PEB) and development in an alkaline developer for10 to 300 seconds, thereby forming a pattern.

EXAMPLE

Examples are given below by way of illustration and not by way oflimitation. The abbreviations Mw and Mn are weight and number averagemolecular weights, respectively, as measured in tetrahydrofuran solventby gel permeation chromatography (GPC) versus polystyrene standards, andMw/Mn is a polydispersity index.

Synthesis Example 1

Fluorinated monomers (1) corresponding to recurring units of formula(1a) which are essential for the polymer to be used as an additivepolymer in resist compositions according to the invention weresynthesized according to the following formulation.

Synthesis Example 1-1

Synthesis of Monomer 1

Synthesis Example 1-1-1

Synthesis of Hemi-Orthoester 1

A flask was charged with 100 g of Fluorinated Alcohol 1, 87 g ofpyridine, and 300 g of acetonitrile. To the contents below 20° C., 232 gof trifluoroacetic anhydride was added dropwise. Stirring was continuedat room temperature for 2 hours, after which the reaction solution waspoured into 300 g of water to quench the reaction. This was followed byordinary aqueous work-up and vacuum distillation, obtaining 126 g ofHemi-Orthoester 1 (yield 87%).

Boiling point: 99° C./21 kPa

IR (D-ATR): ν=3608, 3435, 1777, 1403, 1375, 1281, 1223, 1175, 1153,1079, 1053, 1024, 991, 969, 955, 929, 903, 870, 777, 754, 746, 739, 723,638 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=1.62 (3H, m), 1.74 (3H, m), 10.03 (1H, s)ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, trifluoroacetic acid standard): δ=−84.76(3F, m), −71.97 (3F, m), −70.02 (3F, m) ppm

Synthesis Example 1-1-2

Synthesis of Monomer 1

A flask was charged with 80 g of Hemi-Orthoester 1, 40.2 g oftriethylamine, 3 g of 4-dimethylaminopyridine, and 160 g ofacetonitrile. To the contents below 20° C., 31.2 g of methacrylic acidchloride in 80 g of acetonitrile was added dropwise. Stirring wascontinued at room temperature for 4 hours, after which the reactionsolution was poured into 240 g of water and 360 g of a 9/1 mixture ofhexane and diethyl ether to quench the reaction. This was followed byordinary aqueous work-up and vacuum distillation, obtaining 61 g of thetarget compound (yield 75%).

Boiling point: 85° C./1.3 kPa

IR (D-ATR): ν=1762, 1639, 1488, 1459, 1441, 1383, 1298, 1253, 1195,1158, 1142, 1110, 1074, 1021, 1009, 970, 953, 928, 872, 858, 826, 805,750, 722, 698, 678, 666, 625 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=1.71 (3H, m), 1.74 (3H, m), 1.89 (3H, s),5.96 (1H, m), 6.13 (1H, s) ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, trifluoroacetic acid standard): δ=−79.59(3F, m), −72.16 (3F, m), −69.97 (3F, m) ppm

Synthesis Example 1-2

Synthesis of Monomer 2

Monomer 2 was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using acrylic acid chloride instead of methacrylic acidchloride. Yield 83%.

Synthesis Example 1-3

Synthesis of Monomer 3

Monomer 3 was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using α-trifluoromethylacrylic acid chloride instead ofmethacrylic acid chloride. Yield 80%.

Synthesis Example 1-4

Synthesis of Monomer 4

Monomer 4 was synthesized by the same procedure as in Synthesis Example1-1 aside from using pentafluoropropionic anhydride instead oftrifluoroacetic anhydride. Two-step yield 71%.

Synthesis Example 1-5

Synthesis of Monomer 5

Monomer 5 was synthesized by the same procedure as in Synthesis Example1-1 aside from using Fluorinated Alcohol 2 instead of FluorinatedAlcohol 1. Two-step yield 70%.

Boiling point: 44-45° C./15 Pa

IR (D-ATR): ν=2970, 2935, 2888, 1761, 1639, 1456, 1440, 1406, 1382,1296, 1249, 1208, 1166, 1123, 1102, 1073, 1021, 998, 978, 950, 929, 906,871, 804, 750, 718, 694, 640, 602 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=1.65 (1H, m), 1.74-1.95 (4H, m), 1.88(3H, s), 2.16-2.19 (3H, m), 5.96 (1H, m), 6.13 (1H, s) ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, trifluoroacetic acid standard): δ=−80.34(3F, m), −73.10 (3F, m), −71.29 (3F, m) ppm

Synthesis Example 1-6

Synthesis of Monomer 6

Synthesis Example 1-6-1

Synthesis of Monomer 6 via Route 1

Monomer 6 was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using methacryloyloxyacetic acid chloride instead ofmethacrylic acid chloride. Yield 72%.

Boiling point: 72° C./11 Pa

IR (D-ATR): ν=1810, 1733, 1639, 1487, 1455, 1421, 1403, 1385, 1321,1298, 1253, 1197, 1158, 1146, 1119, 1084, 1061, 1018, 995, 971, 952,857, 814, 751, 722, 689, 672, 650, 616, 603, 585, 568 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=1.75 (6H, m), 1.90 (3H, m), 4.97 (2H, m),5.81 (1H, m), 6.12 (1H, m) ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, trifluoroacetic acid standard): δ=−80.11(3F, m), −72.07 (3F, s), −69.63 (3F, m) ppm

Synthesis Example 1-6-2

Synthesis of Monomer 6 via Route 2

Monomer 6 was synthesized by the alternative procedure of Route 2.

Synthesis Example 1-6-2-1

Synthesis of Halo-Ester

Halo-Ester was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using 2-chloroacetic acid instead of methacrylic acidchloride. Yield 64%.

Boiling point: 102° C./13 Pa

IR (D-ATR): ν=1809, 1791, 1488, 1412, 1403, 1384, 1299, 1235, 1197,1159, 1143, 1118, 1081, 1018, 996, 971, 925, 858, 838, 810, 755, 722,677, 631, 616, 558 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=1.65 (1H, m), 1.75 (6H, m), 4.68 (2H, s)ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, trifluoroacetic acid standard): δ=−79.97(3F, m), −72.14 (3F, s), −69.73 (3F, m) ppm

Synthesis Example 1-6-2-2

Synthesis of Monomer 6

A flask was charged with 80 g of Halo-Ester, 34.5 g of methacrylic acid,and 240 g of N,N-dimethylformamide. To the contents below 20° C., 30.4 gof triethylamine was added dropwise, followed by stirring at roomtemperature for 4 hours. By work-up as in Synthesis Example 1-1-2,Monomer 6 was recovered (yield 74%).

Synthesis Example 1-7

Synthesis of Monomer 7

Monomer 7 was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using acryloyloxyacetic acid chloride instead ofmethacrylic acid chloride. Yield 74%.

Synthesis Example 1-8

Synthesis of Monomer 8

Monomer 8 was synthesized by the same procedure as in Synthesis Example1-1 aside from using pentafluoropropionic anhydride instead oftrifluoroacetic anhydride and methacryloyloxyacetic acid chlorideinstead of methacrylic acid chloride. Yield 69%.

Synthesis Example 1-9

Synthesis of Monomer 9

Monomer 9 was synthesized by the same procedure as in Synthesis Example1-1-2 aside from using Hemi-Orthoester 2 (Synthesis Example 1-5) insteadof Hemi-Orthoester 1 and methacryloyloxyacetic acid chloride instead ofmethacrylic acid chloride. Yield 73%.

Monomers 1 to 9 of Synthesis Examples are identified below by theirstructural formula.

Synthesis Example 2

Polymers were synthesized according to the following formulation.

Synthesis Example 2-1

Synthesis of Polymer 1

In a nitrogen atmosphere, a flask was charged with 10.70 g of Monomer 6,4.59 g of 4,4,4-trifluoro-3-hydroxy-2-methyl-3-trifluoromethylbutan-2-ylmethacrylate, 0.45 g of dimethyl 2,2′-azobis(isobutyrate), and 15 g of a9/1 mixture of toluene and methyl ethyl ketone to form a monomersolution at a temperature of 20-25° C. In a nitrogen atmosphere, anotherflask was charged with 7.5 g of a 9/1 mixture of toluene and methylethyl ketone, which was heated at 80° C. with stirring. The monomersolution was added dropwise thereto over 4 hours. After the completionof dropwise addition, the solution was stirred for a further 2 hours forpolymerization while maintaining the temperature of 80° C. At the end ofmaturing, the solution was cooled to room temperature and added dropwiseto 150 g of hexane whereupon a copolymer precipitated. The copolymer wascollected by filtration, washed with 90 g of hexane, and separated as awhite solid. The white solid was vacuum dried at 50° C. for 20 hours,yielding the target polymer, designated Polymer 1, in white powder solidform. Amount 11.6 g, yield 74%.

Synthesis Examples 2-2 to 2-19 and Comparative Synthesis Examples 1-1 to1-3

Synthesis of Polymers 2 to 19 and Comparative Polymers 20 to 22

Polymers were synthesized by the same procedure as in Synthesis Example2-1, aside from changing the type and amount of monomers. It is notedthat the values of formulation in Table 1 are molar ratios of monomerunits. The structures of units in Table 1 are shown in Table 2.

TABLE 1 Unit 1 Unit 2 Unit 3 Polymer (ratio) (ratio) (ratio) MwSynthesis 2-1 Polymer 1 Y-3M Y-7M — 8,700 Example (0.60) (0.40) 2-2Polymer 2 Y-1M Y-7M — 5,200 (0.60) (0.40) 2-3 Polymer 3 Y-2M Y-7M —5,300 (0.60) (0.40) 2-4 Polymer 4 Y-4M Y-7M — 8,800 (0.60) (0.40) 2-5Polymer 5 Y-5M Y-7M — 8,900 (0.60) (0.40) 2-6 Polymer 6 Y-6M Y-7M —8,900 (0.60) (0.40) 2-7 Polymer 7 Y-3M Y-8M — 8,900 (0.60) (0.40) 2-8Polymer 8 Y-3M Y-7M Y-9M  8,900 (0.40) (0.40) (0.20) 2-9 Polymer 9 Y-3MY-7M Y-10M 8,900 (0.40) (0.40) (0.20) 2-10 Polymer 10 Y-3M Y-7M Y-11M8,700 (0.40) (0.40) (0.20) 2-11 Polymer 11 Y-3M Y-7M Y-12M 8,900 (0.40)(0.40) (0.20) 2-12 Polymer 12 Y-3M Y-7M Y-13M 9,000 (0.40) (0.40) (0.20)2-13 Polymer 13 Y-3M Y-7M Y-14M 8,900 (0.40) (0.40) (0.20) 2-14 Polymer14 Y-4M Y-7M Y-9M  8,900 (0.40) (0.40) (0.20) 2-15 Polymer 15 Y-4M Y-7MY-10M 8,900 (0.40) (0.40) (0.20) 2-16 Polymer 16 Y-4M Y-7M Y-11M 8,800(0.40) (0.40) (0.20) 2-17 Polymer 17 Y-4M Y-7M Y-12M 8,900 (0.40) (0.40)(0.20) 2-18 Polymer 18 Y-4M Y-7M Y-13M 9,100 (0.40) (0.40) (0.20) 2-19Polymer 19 Y-4M Y-7M Y-14M 8,900 (0.50) (0.40) (0.10) Comparative 1-1Polymer 20 — Y-7M — 8,700 Synthesis (1.00) Example 1-2 Polymer 21 — Y-7MY-11M 9,000 (0.40) (0.60) 1-3 Polymer 22 — Y-7M Y-15M 9,100 (0.40)(0.60)

TABLE 2

Y-1M (R = CH₃)

Y-2M (R = CH₃)

Y-3M (R = CH₃)

Y-4M (R = CH₃)

Y-5M (R = CH₃)

Y-6M (R = CH₃)

Y-7M (R = CH₃)

Y-8M (R = CH₃)

Y-9M (R = CH₃)

Y-10M (R = CH₃)

Y-11M (R = CH₃)

Y-12M (R = CH₃)

Y-13M (R = CH₃)

Y-14M (R = CH₃)

Y-15M (R = CH₃)

Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-4

Evaluation of Resist

A resist solution was prepared by dissolving 5 g of Resist Polymer(shown below), 0.25 g of an additive polymer selected from Polymers 1 to22, 0.25 g of PAG1 (shown below), and 0.05 g of Quencher 1 (shown below)in 75 g of PGMEA and filtering through a polypropylene filter having apore size of 0.2 μm. In Comparative Example 1-4, a resist solution wassimilarly prepared aside from omitting the additive polymer.

An antireflective coating ARC-29A (Nissan Chemical Co., Ltd.) wasdeposited on a silicon substrate to a thickness of 87 nm. The resistsolution was applied onto the ARC and baked at 90° C. for 60 seconds toform a resist film of 90 nm thick.

A contact angle with water of the resist film was measured, using aninclination contact angle meter Drop Master 500 by Kyowa InterfaceScience Co., Ltd. Specifically, the wafer covered with the resist filmwas kept horizontal, and 50 μL of pure water was dropped on the resistfilm to form a droplet. While the wafer was gradually inclined, theangle (sliding angle) at which the droplet started sliding down wasdetermined as well as receding contact angle. The results are shown inTable 3.

A smaller sliding angle indicates an easier flow of water on the resistfilm. A larger receding contact angle indicates that fewer liquiddroplets are left during high-speed scan exposure. It is demonstrated inTable 3 that the inclusion of the additive polymer of the invention in aresist solution achieves a drastic improvement in the receding contactangle of photoresist film without adversely affecting the sliding angle,as compared with those photoresist films free of the additive polymer.

Also, the resist film-bearing wafer (prepared above) was irradiatedthrough an open frame at an energy dose of 50 mJ/cm² using an ArFscanner S305B (Nikon Corp.). Then a true circle ring of Teflon® havingan inner diameter of 10 cm was placed on the resist film, 10 mL of purewater was carefully injected inside the ring, and the resist film waskept in contact with water at room temperature for 60 seconds.Thereafter, the water was recovered, and a concentration of photoacidgenerator (PAG1) anion in the water was measured by an LC-MS analyzer(Agilent). The results are also shown in Table 3.

It is evident from Table 3 that a photoresist film formed from a resistsolution containing the additive polymer according to the invention iseffective in inhibiting the PAG from being leached out of the film inwater.

Further, the resist film-bearing wafer (prepared above) was exposed bymeans of an ArF scanner model S307E (Nikon Corp., NA 0.85, σ0.93, ⅘annular illumination, 6% halftone phase shift mask), rinsed for 5minutes while splashing pure water, post-exposure baked (PEB) at 110° C.for 60 seconds, and developed with a 2.38 wt % TMAH aqueous solution for60 seconds, forming a 75-nm line-and-space pattern. The wafer wassectioned, and the profile and sensitivity of the 75-nm line-and-spacepattern were evaluated. The results are also shown in Table 3.

As seen from Table 3, when exposure is followed by water rinsing, theresist film having the additive polymer according to the inventionformulated therein formed a pattern of rectangular profile, in starkcontrast with the resist film free of the additive polymer forming apattern of T-top profile.

TABLE 3 Contact angle Receding Anion with water Sliding contact leach-75-nm after Additive angle angle out Sensitivity pattern developmentPolymer (°) (°) (ppb) (mJ/cm²) profile (°) Example 1-1 Polymer 1 13 86 631 rectangular 48 Example 1-2 Polymer 2 15 78 7 31 rectangular 74Example 1-3 Polymer 3 13 79 6 31 rectangular 76 Example 1-4 Polymer 4 1186 6 31 rectangular 49 Example 1-5 Polymer 5 12 87 6 31 rectangular 48Example 1-6 Polymer 6 12 88 6 31 rectangular 48 Example 1-7 Polymer 7 1386 6 31 rectangular 48 Example 1-8 Polymer 8 14 82 6 31 rectangular 49Example 1-9 Polymer 9 13 84 6 31 rectangular 48 Example 1-10 Polymer 1014 82 7 32 rectangular 42 Example 1-11 Polymer 11 11 87 6 31 rectangular60 Example 1-12 Polymer 12 12 86 6 30 rectangular 50 Example 1-13Polymer 13 11 90 6 31 rectangular 45 Example 1-14 Polymer 14 14 81 6 31rectangular 49 Example 1-15 Polymer 15 13 84 6 31 rectangular 48 Example1-16 Polymer 16 14 81 7 32 rectangular 42 Example 1-17 Polymer 17 11 876 31 rectangular 60 Example 1-18 Polymer 18 12 87 6 30 rectangular 50Example 1-19 Polymer 19 11 89 6 31 rectangular 45 Comparative Polymer 2020 56 5 33 rectangular 37 Example 1-1 Comparative Polymer 21 18 63 9 33rectangular 25 Example 1-2 Comparative Polymer 22 18 72 8 33 rectangular28 Example 1-3 Comparative — 28 39 60 31 T-top 75 Example 1-4

Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3

Evaluation of Development Defects

Some resist solutions used in the patterning experiment were precisionfiltered through a high-density polyethylene filter with a pore size of0.02 μm. An antireflective coating ARC-29A (Nissan Chemical Co., Ltd.)of 87 nm thick was deposited on a 8-inch silicon substrate. The resistsolution was applied onto the ARC and baked at 90° C. for 60 seconds toform a resist film of 90 nm thick. Using an ArF scanner model S307E(Nikon Corp., NA 0.85, Q 0.93, Cr mask), the entire surface of the waferwas subjected to checkered-flag exposure including alternate exposure ofopen-frame exposed and unexposed portions having an area of 20 mmsquare. This was followed by post-exposure baking (PEB) and developmentwith a 2.38 wt % TMAH aqueous solution for 60 seconds. Using a flawdetector Win-Win 50-1200 (Tokyo Seimitsu Co., Ltd.), the number of blobdefects in the unexposed portion of the checkered-flag was counted atthe pixel size of 0.125 μm. The results are shown in Table 4.

TABLE 4 Additive polymer Number of defects Example 2-1 Polymer 1 800Example 2-2 Polymer 4 800 Example 2-3 Polymer 10 400 Comparative Example2-1 Polymer 20 >10,000 Comparative Example 2-2 Polymer 22 3,500Comparative Example 2-3 not added >10,000

It is evident from Table 4 that in the resist film from the resistsolution free of the additive polymer, numerous development defects wereobserved after the immersion lithography. The defects could not beobviated by adding Polymer 20 or 22. The resist solution containing theadditive polymer (Polymer 1, 4 or 10) according to the invention waseffective in minimizing such defects.

Japanese Patent Application No. 2010-088537 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A polymer comprising recurring units of thegeneral formula (1a):

wherein R¹ is hydrogen, fluorine, methyl or trifluoromethyl, R² and R³are each independently hydrogen or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R² and R³ may bond together to form anon-aromatic ring with the carbon atom to which they are attached, R⁴ toR⁶ each are a C₁-C₆ monovalent fluorinated hydrocarbon group, A is astraight, branched or cyclic C₁-C₁₀ divalent hydrocarbon group, and k¹is an integer of 0 to
 2. 2. A resist composition comprising (A) apolymer comprising recurring units of the general formula (1a)

wherein R¹ is hydrogen, fluorine, methyl or trifluoromethyl, R² and R³are each independently hydrogen or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R² and R³ may bond together to form anon-aromatic ring with the carbon atom to which they are attached, R⁴ toR⁶ each are a C₁-C₆ monovalent fluorinated hydrocarbon group, A is astraight, branched or cyclic C₁-C₁₀ divalent hydrocarbon group, and k¹is an integer of 0 to 2, (B) a polymer having a lactone ring-derivedstructure, hydroxyl-containing structure and/or maleic anhydride-derivedstructure as a base resin, said base polymer becoming soluble inalkaline developer under the action of acid, (C) a compound capable ofgenerating an acid upon exposure to high-energy radiation, and (D) anorganic solvent.
 3. A resist composition comprising (A) a polymercomprising recurring units of the general formula (1a) as set forth inclaim 1 and recurring units of one or more type selected from thegeneral formulae (2a) to (2i), (B) a polymer having a lactonering-derived structure, hydroxyl-containing structure and/or maleicanhydride-derived structure as a base resin, said base polymer becomingsoluble in alkaline developer under the action of acid, (C) a compoundcapable of generating an acid upon exposure to high-energy radiation,and (D) an organic solvent,

wherein R¹ is as defined above, R^(4a) and R^(4b) each are hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, orR^(4a) and R^(4b) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon atom to which they are attached, R^(5a)is hydrogen, a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon or fluorinated hydrocarbon group, or an acid labile group,in the case of hydrocarbon group, any constituent moiety —CH₂— may bereplaced by —O— or —C(═O)—, R^(6a), R^(6b) and R^(6c) each are hydrogen,or a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group,R^(6a) and R^(6b), R^(6a) and R^(6c), R^(6b) and R^(6c) may bondtogether to form a non-aromatic ring of 3 to 8 carbon atoms with thecarbon atom to which they are attached, R^(7a) is hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, R^(7b)is a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group,R^(7a) and R^(7b) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon and oxygen atoms to which they areattached, R^(8a) is a straight, branched or cyclic C₁-C₁₅ monovalentfluorinated hydrocarbon group, R^(9a) is a straight, branched or cyclicC₁-C₁₀ monovalent fluorinated hydrocarbon group, R^(10a) is a straight,branched or cyclic C₁-C₁₅ monovalent hydrocarbon group which may containhalogen or oxygen, and k² is 0 or
 1. 4. The resist composition of claim2 wherein the polymer (B) is selected from the group consisting of(meth)acrylate polymers, (α-trifluoromethyl)acrylate-maleic anhydridecopolymers, cycloolefin-maleic anhydride copolymers, polynorbornene,polymers resulting from ring-opening metathesis polymerization ofcycloolefins, hydrogenated polymers resulting from ring-openingmetathesis polymerization of cycloolefins, polyhydroxystyrene,copolymers of hydroxystyrene with one or more (meth)acrylate, styrene,vinylnaphthalene, vinylanthracene, vinylpyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, indene, hydroxyindene, acenaphthylene, ornorbornadiene derivatives, and novolac resins.
 5. The resist compositionof claim 2 wherein the polymer (B) comprises recurring units of at leastone type selected from the general formulae (2A) to (2D):

wherein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA isan acid labile group, XB and XC each are a single bond or a straight orbranched C₁-C₄ divalent hydrocarbon group, YA is a substituent grouphaving a lactone structure, ZA is hydrogen, or a C₁-C₁₅ fluoroalkylgroup or C₁-C₁₅ fluoroalcohol-containing substituent group, and k^(1A)is an integer of 1 to
 3. 6. The resist composition of claim 2 whereinthe polymer (A) comprising recurring units of formula (1a) is added inan amount of 0.1 to 50 parts by weight per 100 parts by weight of thepolymer (B).
 7. The resist composition of claim 2, further comprising(E) a basic compound.
 8. The resist composition of claim 2, furthercomprising (F) a dissolution regulator.
 9. A pattern forming processcomprising the steps of (1) applying the resist composition of claim 2onto a substrate to form a resist coating, (2) heat treating the resistcoating and exposing it to high-energy radiation through a photomask,and (3) developing the exposed coating with a developer.
 10. A patternforming process comprising the steps of (1) applying the resistcomposition of claim 2 onto a substrate to form a resist coating, (2)heat treating the resist coating and exposing it to high-energyradiation from a projection lens through a photomask while holding aliquid between the substrate and the projection lens, and (3) developingthe exposed coating with a developer.
 11. A pattern forming processcomprising the steps of (1) applying the resist composition of claim 2onto a substrate to form a resist coating, (2) forming a protectivecoating onto the resist coating, (3) heat treating the resist coatingand exposing it to high-energy radiation from a projection lens througha photomask while holding a liquid between the substrate and theprojection lens, and (4) developing with a developer.
 12. The process ofclaim 10 wherein the liquid is water.
 13. The process of claim 9 whereinthe high-energy radiation has a wavelength in the range of 180 to 250nm.
 14. A pattern forming process comprising the steps of (1) applyingthe resist composition of claim 2 onto a mask blank to form a resistcoating, (2) heat treating the resist coating and exposing it in vacuumto electron beam, and (3) developing with a developer.
 15. The resistcomposition of claim 2, comprising an additive polymer of the formula

wherein c=0.60 and d=0.40, said additive polymer having a weight-averagemolecular weight of 8700, and a resist polymer of the formula

said resist polymer having a weight-average molecular weight of 7400 anda ratio of a weight-average molecular weight to number-average molecularweight of 1.8.